The effects of dietary components, other exogenous factors and age on the development and function of the mammary gland have recently received increased attention. In addition, considerable attention has been devoted to the molecular mechanism(s) of hormone action in the control of growth and developmental processes. Studies involving the mammary gland, dietary modifications and the aging process are becoming crucial because of the: 1) relatively high incidence of cancer development associated with increased fat and/or age, 2) increased knowledge of the hormonally controlled morphological and biochemical transformations intrinsic in mammary gland differentiation and 3) increased tendency of the human female to delay conception (primiparous pregnancy) until the late adult stage. It is important to understand that interpretations of dietary and hormonal effects on the morphology, physiology and biochemistry of the mammary gland require consideration of the developmental state or age of the organism. It is important to recognize variations in tissue sensitivity to nutrients and hormones as well as the time during development when the tissue develops and/or loses the capacity to respond to endogenous and oxgeneous factors of the molecular level. The present investigation addresses several of the above concerns i.e., 1) the action of dietary fats and carbohydrates on mammary gland function and milk fat composition at various age levels, 2) the effects of dietary modifications on hormone control mechanism during induced lactogenesis, 3) dietary-induced changes in the activity of lopgenic enzymes, 4) influence of neonatal exposure to dietary modification and subsequent mammary gland development and 5) significance of dietary modifications and age in the development and has been devoted to the molecular mechanism(s) of hormone action in the control of growth and developmental processes. Studies involving the mammary gland, dietary modifications and the aging process are becoming crucial because of the: 1) relatively high incidence of cancer development associated with increased fat and/or morphological and biochemical transformations intrinsic in mammary gland differentiation and 3) increased tendency of the human female to delay conception (primiparous pregnancy) until the late adult stage. It is important to understand that interpretations of dietary and hormonal effects on the morphology, physiology and biochemistry of the mammary gland require consideration of the hormone-tissue and nutrient-tissue interaction in addition to the developmental state or age of the organism. It is important to recognize variations in tissue sensitivity to nutrients and hormones as well as the time during development when the tissue develops and/or loses the capacity to respond to endogenous and oxgeneous factors of the molecular level.